For a few years on the Web I saw this article titled "How a Story is Shaped" resurface time and time again, and with good reason. It's a succinct and accurate analysis of typical Western narrative (Western Hemisphere, mind you, not Western as in John Wayne or Clint Eastwood). Author Lynn Maupin Webb describes how stories as disparate as Snow White, Romeo and Juliet, ET, Indiana Jones, and Pulp Fiction rely upon common elements for narrative flow.
If you're a teacher who feels that your students' stories are often rambling and pointless excursions, it may be time to provide them with a proper scaffold. Once they see for themselves that many effective stories share this pattern, their own attempts will be more purposeful and satisfying.